Given the information on the proble, we can use the formula for simple interest to find the principal amount to be invested:
where P represents the principal amount, r the interest rate, t represents the time and A is the total amount.
In this case we know that A = 12000, since that is the price of the car in four years. With r = 7.3% = 0.073 and t = 4, we have:
therefore, the amount to be invested is $9287.93